Advantages and disadvantages of Frequency Division Duplex (FDD) and Time Division Duplex (TDD) are as follows. The FDD is suitable for a service such as voice which generates symmetric traffic, and the TDD is suitable for a service such as Internet or data, which is bursty and has asymmetric traffic. The TDD utilizes a spectrum more efficiently. The FDD cannot be used in an environment where a service provider has no sufficient bandwidth for offering a guardband required between transmit and receive channels. The TDD is more flexible than the FDD in satisfying a demand for dynamically configuring an uplink and a downlink in response to customer needs.
Carrier Aggregation (CA) is a technique defined in a Long Term Evolution (LTE)-Advanced (A) system. The CA enables aggregation of multiple carriers so as to attain a wider overall system bandwidth. Thus, a peak data rate of the system can increase. In current, only the CA of TDD carriers and the CA of FDD carriers are supported and there are no standards or techniques for combining the TDD carriers and the FDD carriers.